1. Field of the Invention
The present invention relates to a head chip that is mounted on an ink jet recording device applied to, for example, a printer or a facsimile.
2. Description of the Related Art
Conventionally, there is known an ink jet recording device that records characters and images on a medium to be recorded using an ink jet head having a plurality of nozzles for discharging ink. In such an ink jet recording device, the nozzles of the ink jet head are provided in a head holder so as to oppose the medium to be recorded, and this head holder is mounted on a carriage to be scanned in a direction perpendicular to a conveying direction of the medium to be recorded.
A sectional view in the longitudinal direction of an example of a head chip of such an ink jet head is shown in FIG. 16A and a sectional view of a main portion of the same is shown in FIG. 16B. As shown in FIGS. 16A and 16B, a plurality of grooves 102 are provided in parallel with each other in a piezoelectric ceramic plate 101, and each groove 102 is separated by sidewalls 103. An end portion in the longitudinal direction of each groove 102 is extended to an end surface of the piezoelectric ceramic plate 101 and the other end portion is not extended to the other end surface, making the groove 102 to be gradually shallow. In addition, electrodes 105 for applying a driving electric field are formed on surfaces on opening side of both sidewalls 103 in each groove 102 throughout its longitudinal direction.
In addition, a cover plate 107 is joined on the opening side of the grooves 102 of the piezoelectric ceramic plate 101 via a partitioning portion using an adhesive 109. The cover plate 107 includes a common ink chamber 111 in the form of a recessed portion communicating with each groove 102 via communication holes provided in the partitioning portion in the longitudinal direction of the respective grooves 102 and an ink supply port 112 that is bored from the bottom portion of the common ink chamber 111 in the direction opposite to the grooves 102.
In addition, a nozzle plate 115 is joined to an end surface of the joined body of the piezoelectric ceramic plate 101, the partitioning portion and the cover plate 107 in which the grooves 102 are opened, and nozzle openings 117 are formed in the nozzle plate 115 at positions opposing the respective grooves 102.
Further, a wiring substrate is fixed to the surface of the piezoelectric ceramic plate 101 on the opposite side of the nozzle plate 115 and on the opposite side of the cover plate 107. Wiring connected to each electrode 105 via bonding wires 121 or the like is formed on the wiring substrate, and a driving voltage can be applied to the electrodes 105 via the wiring.
In a head chip configured in this way, when each groove 102 is filled with ink from the ink supply port 112 and a predetermined driving electric field is caused to act on the sidewalls 103 on both sides of the predetermined groove 102 via the electrode 105, the sidewalls 103 are deformed to change the capacity inside the predetermined groove 102, whereby the ink in the groove 102 is discharged from the nozzle opening 117.
For example, as shown in FIG. 17, if ink is discharged from the nozzle opening 117 corresponding to a groove 102a, a positive driving voltage is applied to electrodes 105a and 105b in the groove 102a and, at the same time, opposing electrodes 105c and 105d to the respective electrodes are grounded. Consequently, a driving electric field in the direction toward the groove 102a acts on sidewalls 103a and 103b and, if the driving electric field is perpendicular to a direction of polarization of the piezoelectric ceramic plate 101, the sidewalls 103a and 103b are deformed in the direction of the groove 102a by a piezoelectric thickness slip effect and the capacity inside the groove 102a decreases to increase pressure, whereby the ink is discharged from the nozzle opening 117.
As a measure for solving a problem that it is difficult to achieve high speed consecutive discharging, that is, to achieve high speed printing in a head chip like this, the degree of sealing of a chamber is increased for the sake of shortening a time from the stoppage of vibration of the sidewalls caused by ink discharging to the obtainment of a situation where pressure of ink in the chamber corresponding to the groove becomes zero to perform the next ink discharging, although this time varies depending on the length of the chamber, the shape of the nozzle opening, and the like. However, if the opening area of the communicating hole is narrowed too much for the sake of enhancing the degree of sealing of the chamber, there occurs a problem that ink necessary for discharging is not sufficiently supplied from the common ink chamber to the chamber and printing is not normally performed.
In view of such circumstances, it is an object of the present invention is to provide a head chip in which the minimum size of the communicating hole, with which it is possible to sufficiently supply ink necessary for discharging and, at the same time, to enhance the degree of sealing of the chamber to a limit, is defined with reference to the length in the longitudinal direction of the chamber.
In order to solve the above-mentioned object, according to a first aspect of the present invention, a head chip includes: a chamber that is defined on a substrate and has an end portion in a longitudinal direction that communicates with a nozzle opening; and an electrode provided on a sidewall of the chamber, in which a driving voltage is applied to the electrode so that a capacity within the chamber is changed to discharge ink filled therein from the nozzle opening. The head chip is characterized in that: an ink chamber plate defining a common ink chamber communicating with the chamber is joined on the substrate; the common ink chamber is provided with a partitioning portion for partitioning the chamber and the common ink chamber; the partitioning portion is provided with a plurality of communicating holes that evenly divide a chamber longitudinal direction of the partitioning portion using a distance between the nozzle opening and a communicating hole establishing communication between the common ink chamber and the chamber and which is provided in the partitioning portion at a position close to the nozzle opening, and each of the plurality of communicating holes has the same opening ratio to an area of the partitioning portion; and if a length in the longitudinal direction of the chamber is referred to as Y (mm) and an opening ratio of each communicating hole to the area of the partitioning portion is referred to as X (%), when a size of the communicating hole satisfying a relation of xe2x80x9cY=xe2x88x924.5X+15.8xe2x80x9d is referred to as Smin and a size of a communicating hole obtained by coupling the plurality of communicating holes to each other is referred to as Smax, there is obtained a relation of Smin size of communicating hole less than Smax.
According to a second aspect of the present invention, in the first aspect of the invention, a head chip is characterized in that the partitioning portion is formed of a separate member.
According to a third aspect of the present invention, in the first or the second aspect of the invention, a head chip is characterized in that the substrate is formed of a piezoelectric ceramic plate, and the chamber is defined by forming a groove in the piezoelectric ceramic plate.
According to a fourth aspect of the present invention, in the first or the second aspect of the invention, a head chip is characterized in that the sidewalls are made of piezoelectric ceramic and are arranged on the substrate at a predetermined interval, and the chamber is defined between the sidewalls.
According to a fifth aspect of the present invention, in the fourth aspect of the invention, a head chip is characterized in that the sidewalls are made of piezoelectric ceramic and are arranged on the substrate at a predetermined interval, and the chamber is defined between the sidewalls, and that the common ink chamber is defined on the substrate, and the chamber and the common ink chamber communicate with each other at one end in the longitudinal direction of the chamber.
In the present invention, the minimum size of the communicating hole, with which it is possible to sufficiently supply ink necessary for discharging and, at the same time, to enhance the degree of sealing of the chamber to a limit, is defined with reference to the length in the longitudinal direction of the chamber. Therefore, it becomes possible to shorten the converging time, during which pressure in the chamber attenuates, without causing the deterioration of an ink supply property and an ink discharging property. As a result, it becomes possible to achieve high speed printing by consecutively discharging ink at high speed.